Ratio circuit



J. P. BLEWETT RATIO CIRCUIT May 15, 1951 Original Filed Oct. 28, 1943 2 Sheets-Sheet; l

y T 1 ww m D lb m 6 MM P m m, a mw W8 2 a R R W M w 0/. W m m m Inventor John I? Blewett, b M 0% His Attorney.

y 15, 1951 J, P. BLEWETT 2,553,294

RATIO CIRCUIT Original Filed Oct. 28, 1943 2 Sheets-Sheet 2 Fig.3.

Ill/P071 Inventor: John P Blewett, b m 43% His Attorney.

i atented May 15, 1951 RATIO CIRCUIT John P. Blewett, East Patchogue, N. Y., assignor to General Electric Company, a corporation of New York Original application October 28, 1943, Serial No.

508,024. Divided and this application December 29, 1945, Serial No. 638,382

2 Claims. (Cl. 171-95) The present invention relates to radio locating equipment utilizing the comparison of echoes arriving at spaced receiving antennas to determine ,the direction of the reflecting object.

This application is a division of my application, Serial No. 508,024, filed October 28, 1943, now Patent 2,467,361, issued April 12, 1949, and assigned to the assignee of this application.

An object of my invention is to provide improved echo comparison circuits and equipment for utilizing the circuits to increase the rate at which information can be obtained.

The novel features which I believe to be characteristic of my invention are et forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a diagram of locating equipment embodying my invention; Figs. 2 and 3 are diagrams of phase comparators, and Figs. 4 and 5 are diagrams of ratio circuits.

Referring to Fig. 1 of the drawings there is shown a parabolic cylinder reflector l fixed at an angle of 45 to a vertical pedestal 2 rotated by a motor 3. Spaced apart along the focal line of the reflector are antennas 4, 5, and 6, the antenna 5 at the center being connected to a pulse transmitter 1 so as to transmit periodic pulses of radio waves each being directed by the reflector in a fan-shaped beam having a width approximately 90.

During the intervals between the transmitted pulse, echoes or reflections from objects located within the plane of the fan-shaped beam arrive at the antennas 4 and 6 at times dependent upon the range of the reflecting objects and with a relative phase dependent upon the direction angle of the reflecting objects measured from the center line of the plane of the transmitted beam. For ground equipment with the center line of the plane of the beam at an elevation of 45, reflections are received from objects at elevations of from 0 to 90 so that the whole sky is scanned during each rotation of the pedestal. The use of phase comparison to determine the elevation of the reflecting objects increases the rate at which information can be obtained.

In the illustrated equipment, the information is presented on the viewing screens 8 and 9 of cathode ray tubes [0, I I, azimuth and range being presented on the viewine screen 8 and azimuth voltages prior to the phase comparison.

2 and elevation being presented on the viewing screen 9.

The map-like presentation on the viewing screen 8 is obtained from the signal picked up by antenna 6, which is fed through a receiver I2 to the grid l3 of the cathode ray tube [0. Around the throat of the cathode ray tube is a deflection coil M fed by a saw-tooth sweep circuit l 5 keyed by the transmitter so as to have a current increasing linearly from a minimum at the end of each transmitted pulse to a maximum immediately prior to a succeeding pulse. The current flowing in the coil 14 causes a radial deflection of the beam of the cathode ray tube starting at the center with each transmitted pulse.

The coil I4 is rotated by the motor 3 synchronously with the pedestal 2 so the deflecting axis corresponds to the azimuth of the fanshaped beam transmitted from the antenna 5.

The radial trace on the viewing screen of the jects, presented on the viewing screen 9, are

obtained by applying the echo signal from re-- ceiver [2 to the grid Hi to modulate the beam of the cathode ray tube II. The beam is deflected horizontally in accordance with the azimuth of the reflecting objects by horiznotal deflection, plates Ilia excited from a potentiometer ll rotated synchronously with the pedestal 2. The beam is deflected vertically in accordance with the elevation of the reflection of objects by vertical deflection plates 55b excited from cir cuits hereinafter described, by voltages dependent upon the relative phase of echoes arriv-- ing at the antennas 4 and 6.

In the phase comparison circuits, the echo sigrials from the antennas 4 and 6 are hetero- .dyned against a common local oscillator 18 in converters l9 andZi) to produce an intermediate frequency of 30 megacycles. Because of the heterodyning against a common local oscillator, the phase difference between the echo signals is preserved at the intermediate frequency. The output of I. F. amplifiers 2! and 22 is fed through a phase comparator 23 and a ratio circuit 24', both hereinafter described, to the deflection plates [1. In accordance with usual practice in phase comparison, a phase shift, indicated at'25, is effected in the relative phase of the The ence voltages.

purpose of the ratio circuit is to make the phase determination independent of variations in the magnitudes of the voltages fed to the phase comparator. This takes care of both the effects of fading which causes both voltages to fluctuate in unison, and of unbalance in the receivin channels, which afiec'ts one voltage more than the other.

In the phase comparator shown in Fig. 2, the output of the I. F. amplifiers 2| and 22 is fed to input transformers 2G and 21 having grounded primary windings 28 and 29 and grounded secondary windings 30a, 36b and 3m, 3 lb. Both the primary and secondary circuits are tuned by shunt condensers 32, 33, 3=l, 35 to the frequency of the voltages to be compared (30 rnegacyclesl and are loaded by shunt resistances 36, 31, 38, 39 to pass a band of about 2 megacycles. This permits the comparison of pulse voltages Such as the echoes from remote objects.

The secondaries 38a, 3m, and 30b, 311) are connected in series, with the instantaneous volt-- ages respectively bucking and aiding as indicated by the voltage arrows on the drawing, by pairs of decoupling impedances 40. At the mid-point of each pair of impedances appear respectively the voltages proportional to the difference and sum of the transformer input voltages. The sum and difference voltages are fed through square law detectors, such as diodes 4| and Q2. The diodes are connected in reverse polarity to ground through condensers as, M which accordingly are charged to voltages of opposite polarityeach proportional to the square of the sum or the difference voltage. The voltage between terminal 45 and ground is proportional to the product of the magnitudes of the voltages to be compared by the sine of the phase displacement between the voltages plus some higher order terms which are negligible if the phase displacement is small. These higher order terms are due to the variation -of the detectors ll and 42 from a'true square law.

By using another pair of diodes Q6 and '41, connected with the same polarity to ground through condensers 48 and 49, the condensers are charged to the square of the respective sum and (liner- At terminal 50 appears a voltage proportional to the sum of the squares of the magnitudes of the voltages to be compared. If E1 and E2 are the magnitudes of the voltages to be compared and is the phase diiference between the voltages Voltage at terminal 45 2E E sin 0 Voltage at terminal 50 E -FE? This equation is equal to sin 0 if E1=E2 and the error in the value of the equation introduced by variations in the voltages E1 or E2 is smaller than the variation in the voltages for reasonable values of E1 or E2. E1 and E2 are ordinarily of very nearly equal magnitude.

One of the advantages of the phase comparison circuit of Fig. 2 is that the input and output -circui'ts can be grounded without introducing errors due to stray capacities. This is particularly important in phase comparison 'athigh frequencies. The grounding is made possible by the connection of each of the pairs of secondaries 30a, 3|a and 38b, 3 lb'in a bridge circuit with one of the pairs of impedanc'e's 40.

In Fig; 3 is a modification of the phase comparisoncircuit of Fig. 2 in which pentodes 5|, 5253, 5 3 have been substituted for the impedances 48 in the bridge circuits between the transformers 6 and 2-1 and the diodes '4 l 142, "46, TI.

The instantaneous potentials with respect to ground across the secondary windings 30a, 30!), 3| a, and SH) are the same as those indicated at Fig. 2 and have been similarly indicated by voltage arrows on Fig. 3 of the drawing. The secondaries 36a. and Sla are connected respectively to the grids 51a and 52a and an amplified output voltage proportional to the sum of the voltages to be compared appears across resistance 55. The secondaries 39b and 3 lb are connected to the control grids of pentodes 53 and 54 and an amplified output voltage proportional to the difference of the voltages to be compared appears across resistance 56. The amplifier output voltages, as in the Fig. 2 circuit, are fed through the diode detectors 4|, 42 to obtain a voltage at terminal 45 proportional to the product of the voltages to be compared by the sine of the phase angle between the voltages. Similarly, from diode detectors 46 and ll a voltage is obtained at terminal 50 proportional to the sum of the squares of the voltages to be compared. Resonant circuits 5'! and 58, which include the diode capacity, increase the proportion of the signal appearing across the diodes.

The amplifiers 5!, 52, 53, 5Q isolate the detector circuits from the input circuits and also permit the regaining of the signal strength sacrineed in the bridge circuits which permit grounding of both the input -and measuring circuits.

It is obvious that unbalance in the circuits will cause inaccuracy. For example, the amplifier tubes 51, '52, 53, 5d should have equal amplification; equal voltages should be induced in the secondaries 30a, 39b, and em, 3), and, for equal input voltages, all of the secondary voltages should be equal, and the resonant circuits at the transformer windings and at the detector input should be tuned to the same frequency.

To obviate the necessity of separately measuring the voltages at terminals 2-5 and 50,- ratio circuits shown in Figs. 4 and 5 may be used to obtain a direct measurement of the quotients of the terminal voltages.

The ratio circuit of Fig. 4 utilizes the characteri-stic's of remote cut-off tubes which over a limited range have an output directly proportional to screen grid voltage and inversely proportional to negative control grid voltage. By using tubes in parallel, this limited range can be extended or made more accurate. The principles are illustrated in Fig. 4 where identical remote cut-off tubes 59 and 66 (e. g. 63K?) are connected in parallel through identical resistances iii and 62. When used in conjunction with the phase comparison circuits of Figs. 2, 3, the con- -trol'gr ids'15 3 and -65 are supplied with a negative direct current voltage equal to E1 +E2 This voltage appears on terminal 59 of Fig. 3, and terminal 59 of Fig.3 may be considered-connected directly to terminal 53 of Fig. 4.. The grounded terminals zfillaa'nd fia'of Fig. 3 maybe considered as directly connected to similarly numbered terminals of Fig. 4. The screen grid 66 is supplied with a fixed positive bias potential E0, as froma source 66a, and the screen grid 65 is supplied with the sum of E0, from source 65a and 2E1E2 sine 6 by a connection from terminal 45 of Fig. 3 to terminal 5 of Fig. 4. The output voltages across resistances 5i and 62 are then each proportional to the quotient of the respective screen grid ivo'lta'ge divided 'by'the #con- 'trol grid voltage, :and a voltmeter 68a connected between .-points'6'l ian'dfifl will continuously indicate tinezsolutionpf :Equa;tiOn 1, It is obvious that the ratio circuit may be used for other voltages. It will handle D.-C. or pulsed voltages and positive and negative ratios. By the use of the ratio circuit, the measurement of phase angle can be made substantially independent of fading or other factors causing fluctuations in magnitude of the voltages to be compared in phase.

The ratio circuit of Fig. 5 which utilizes the characteristics of multivibrators, will handle ratics of D.-C. voltages. erated to indicate the ratio either by the percentage of time one of the multivibrator tubes is conducting or by the output frequency.

The circuit is the conventional multivibrator with identical triodes 69 and 10, condensers H and 12, and grid resistances 13 and 14.

In the first mode of operation, in which the ratio is measured by the percentage of time one of the tubes is conducting, one of the voltages to be compared (V1) is applied to the grid resistance 14 and the other voltage (V2) minus the first voltage is applied to the grid resistance 13, where V1 and V2 are positive unidirectional voltages. Where the ratio circuit is used with a phase comparator such as shown at Fig. 2 or 3, the voltages V1 and V2 are the voltages appearing at the terminals 45 and 50. An ammeter in series with the tube will indicate the ratio of the first voltage to the other voltage. This is based upon the fact that, with identical tubes and RC grid circuits, 1'

the time each tube is cut oil is inversely proportional to the grid voltage.

The time t2 that tube 10 is cut 011 is equal to a constant times 1/V1, since V1 is applied to resistor 14. The time t1 that tube 69 is cut ofi is equal to the same constant times 1/(V2V1), since (V2-Vi) is applied to resistor 13. It will be apparent that 151 is equal to the time tube 79 is conductive, and that where f is the percentage of time that tube '10 is conducting. Substituting 1/V1 for n and 1/(V2-V1) for t2, and reducing the equation, it is found that the percentage of time that tube 10 is conductive, to which the ammeter reading will be proportional, is equal to 2 1 1 1 V V2-v1 v1 In the second mode of operation in which the ratio of the voltages is measured by the output frequency of the multivibrator, use is made of the fact that with a multivibrator having a positive grid bias the output frequency is linearly p'o'r'portional to the ratio of the grid voltage to the plate voltage. If V1 is applied to the grid resist- This circuit can be opances l3 and I4 and V2 is applied to the anodes .15 and 16, the output frequency will be proportional to the ratio V1172.

While I have shown particular embodiments of my invention, it will be understood that many modifications may be made without departing from the spirit thereof, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A ratio circuit for obtaining the ratio of two voltages comprising a pair of remote cut-ofi a amplifier tubes each having control and screen grids, the output of each tube being inversely proportional to voltages applied to one of said grids thereof and directly proportional to voltages applied to the other of said grids thereof, means for supplying equal biasing potentials to said screen grids, means for impressing one of the voltages on both of said control grids in parallel, means for impressing the other of the voltages on one of the screen grids only, an individual output load impedance for each amplifier, and

means connected across said load impedances in series for measuring the difierence between the outputs of the tubes to obtain the ratio of said voltages.

2. A ratio circuit for obtaining the ratio of two voltages comprising a pair of amplifiers both having output currents inversely proportional, over a predetermined control range, to negative control grid voltage and linearly and directly proportional to screen grid voltage, means for applying equal biasing potentials to said screen grids, means applying one of said two voltages to both amplifier control grids in parallel, means for adding the other of said two voltages to the screen grid bias of only one of the amplifiers, an individual output load impedance for each amplifier, and means connected across said load impedances in series for measuring the difference between the amplifier outputs.

JOHN P. BLEWETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,880 Scherbatskoy et al. Sept. 13, 1938 2,154,492 Clough Apr. 18, 1939 2,179,265 Luck Nov. 7, 1939 2,208,378 Luck July 16, 1940 2,256,512 Artzt Sept. 23, 1941 2,306,456 Mayne Dec. 29, 1942 2,358,148 Cook Sept. 12, 1944 2,398,421 Frische et al. Apr. 16, 1946 

